The low rank coal, such as subbituminous coal or brown coal, which has a moisture content higher than about 20 mass % is limited to use within a coal-producing region. This is because, for example, the low rank coal has a low calorific value resulting from its high moisture content and generates a small amount of heat by combustion. On the other hand, when dried, the low rank coal becomes more spontaneously combustible and more hygroscopic, resulting in transportation costs being relatively expensive, etc.
However, the low rank coal has advantages that are not found, e.g., in the bituminous coal that is considered to be a high rank coal. For example, brown coal found in Australia and Indonesia is low in sulfur content and produces less ash. Thus, using the brown coal as a fuel would make it possible to prevent air pollution due to sulfur dioxide gas, etc., as well as to reduce hazardous ash waste.
In this context, such techniques have been suggested which are adopted to carbonize the low rank coal by dehydration reform or thermal reform, thereby compensating for the drawbacks thereof. For example, disclosed in Patent Literature 1 and Patent Literature 2 is a technique by which oil and low rank coal are mixed to obtain raw material slurry; the resulting slurry is heated and dehydrated in the oil, and then further heated to decompose or detach the carboxyl radical or the hydroxyl radical, etc., in the raw material coal by a decarboxylation reaction or a dehydration reaction, thereby reforming the raw material coal. Also disclosed is a technique by which heavy oil, etc., is penetrated into pores of the low rank coal so as to prevent spontaneous combustion.
Further, disclosed in Patent Literature 3 is a method for manufacturing reformed coal and hydrocarbon oil by thermally decomposing brown coal into reformed coal and tar under an inert gas atmosphere or steam atmosphere and catalytically cracking the tar in a steam atmosphere and in the presence of an iron-based catalyst so as to obtain hydrocarbon oil.
Disclosed in Patent Literature 4 is a fixed carbon recycle device in which a plurality of lines are arranged for recycle in recycling the fixed carbon, whereby the flows of the powder materials serve to complement each other, thereby eliminating clogging.